how do you muffle your guitar strings?
I think you mean "palm muting"?
You lightly rest the fleshy part of your picking hand on the strings just past the bridge. Apply more or less preasure to suit the sound you're looking for. To get more of a muffled sound, (like a "chunka chunka" sound), do the palm mute and also rest your fretting hand fingers lightly over the strings.
Here's some youtube links to check out:
http://www.youtube.com/results?search_query=palm+muting&search=Search
Dan
"The only way I know that guarantees no mistakes is not to play and that's simply not an option". David Hodge
While I prefer the palm mute, an alternative is to use a free finger on the fretting hand to dampen a string or two or to lift the fret hand slightly off the strings. How much pressure to apply is a case of trial and error as well as personal preference. Shuffles are a good way to practice. Over on YouTube is a set of lessons by someone called deltabluestips who goes over techniques to dampen strings
